Fuel injector

ABSTRACT

An inwardly opening pressure actuated liquid fuel injector is provided with a tubular body having a valve guide for mounting a valve for reciprocating movement toward and away from a valve seat. A coil spring biases the valve toward its seat and has a spring seat captured in the end thereof with a flat surface engaging the flat end of the valve for free relative lateral movement to avoid imposing lateral forces on the valve. A lift stop has a stem extending through the coil spring and has a close sliding fit therewith to keep the spring coaxial with the stem. The spring seat is spaced from the wall of the spring chamber to prevent contact with the wall and the end of the stem has a slight taper to provide for limited lateral movement and to resiliently bias the spring seat toward a coaxial position with the stem.

United States Patent 1191 Tolan 1451 Apr. 23, 1974 1 FUEL INJECTOR [75] Inventor: Lewis Eric Tolan, Simsbury, Conn. [73] Assignee: Stanadyne, lnc., Hartford, Conn.

[22] Filed: Apr. 24, 1972 [21] Appl. No.: 246,528

Primary Examiner-M. Henson Wood, Jr. Assistant Exa m irte rJohn ,L Love Attorney, Agent, or Firm-Prutzmam Hayes/Kalb 8i:

Chilton l 5 ABSTRACT An inwardly opening pressure actuated liquid fuel injector is provided with a tubular body having a valve guide for mounting a valve for reciprocating movement toward and away from a valve seat.

A coil spring biases the valve toward its seat and has a spring seat captured in the end thereof with a flat surface engaging the flat end of the valve for free relative lateral movement to avoid imposing lateral forces on the valve. A lift stop has a stem extending through the coil spring and has a close sliding fit therewith to keep the spring coaxial with the stem.

The spring seat is spaced from the wall of the spring chamber to prevent contact with the wall and the end of the stemhas a slight taper to provide for limited lateral movement and to resiliently bias the spring seat toward a coaxial position with the stem.

'3 Claims, 1 Drawing Figure lll FUEL INJECTOR This invention relates generally to fuel injectors for compression-ignition engines and is more particularly concerned with an improvement in an injector of the type described in US. Pat. No. 3,255,974, issued June 14, 1966, and entitled Fuel Injection Nozzle.

In inwardly opening pressure actuated liquid fuel injectors of the type contemplated by this invention, the plunger or valve is lifted from its seat by the pressure of fuel which may be delivered to the bore of the injector by an associated high pressure pump in measured quantities or charges. Each measured charge of pressurized fuel is delivered by the injector to the combustion chamber of an associated engine and the discharge of fuel by the injector is timed to take place during a precise interval of time during the compression stroke of the piston in the combustion chamber. To achieve this result, it is essential that the valve of the injector not be subject to seizure or bindingin its guide, as may occur as a result of side thrust on the valve, under all operating conditions.

A primary object of the present invention is to provide an improved injector of the type described having a reduced susceptibility of valve seizure and other malfunctions under all operating conditions.

A further object of this invention is to provide an improved injector for a compression-ignition engine having a hydraulic pressure responsive reciprocating valve controlled by a biasing spring construction which minimizes the lateral thrust imposed on the valve and is inexpensive to manufacture.

Other objects will be in part obvious and in part pointed out more in detail hereinafter.

The invention accordingly consists in the features of construction, combination of elements, and arrangement of parts which are exemplified in a construction hereinafter set forth.

In the drawing, the single FIGURE is a side elevational view, partly broken away, of an exemplary injector incorporating this invention.

The exemplary injector illustrated in the drawing comprises an elongated generally tubular body having a discharge tip 12 at one end thereof and a central longitudinal bore 14. A plunger or valve 16 having a conical tip 18 which engages a conical valve seat 20 to control the discharge of fuel from the injector is positioned in the central bore 14. A lapped portion of the upper end of the valve 16 forms a cylindrical guide portion 21 which is received within a lapped complementary guide 22 of the injector body 10 at a position remote from the valve seat to slidably mount the valve 16 in coaxial alignment with the valve seat 20.

The injector is provided with a fuel inlet 24 communicating with the bore 14 of the tubular body 10 for the delivery of discrete measured charges of high pressure fuel thereto from a source (not shown). A spring 26, disposed in spring chamber 28 above the valve guide 22, biases the valve downwardly against the valve seat 20. The biasing pressure imposed on the valve 16 may be adjusted by shims 30 placed between the spring 26 and the internally and externally threaded adjusting sleeve 32 which threadably engages the threaded end of the tubular body 10. An adjustable lift stop 34 is provided with a stem 35 to limit the lift of the valve 16 from the valve seat 20 and is locked in place by a lock nut 36.

When a charge of pressurized fuel delivered to the injector increases the pressure of the fuel therein to a level sufficient to overcome the bias of spring 26, the valve 16 is lifted from the seat 20 and the charge of fuel is discharged through the orifices 37 of the valve tip 12 into a combustion chamber of the associated engine.

It is important for smooth operation of the associated engine, that the plunger 16 be free to reciprocate rapidly so that the valve movement is not delayed due to friction or any seizure or binding of the valve 16 and the valve guide 22. The valve seat 20 and the valve guide 22 are coaxially aligned to minimize any binding due to lateral forces which might be imposed on the valve as a result of any misalignment of the valve seat. However, lateral forces may also be imposed on the valve because of a lack of coaxiality of the spring 26 and the valve 16 or by a lack of squareness in the ends of the spring.

In a four-cycle compression-ignition engine, the period generally available for the injection of a charge of fuel during each compression stroke is approximately 20 out of every 720 of crankshaft rotation. With such an engine operating at, say, 3,000 rpm, the period of time for injection of a charge of fuel is about 0.001 1 1 second. It is readily apparent that any variation in fric tion between the valve 16 and its guide 22 or any variation of the biasing force of spring can significantly effect injection and the smoothness of operation of the associated engine.

A feature of this invention is the provision of an easy to manufacture biasing spring construction, which is self-aligning and stable, and in which the lateral forces imposed on the valve are minimized, despite any lack of squareness of the ends of the spring 26 or any axial misalignment between the valve 16 and the spring 26.

As shown, the end 39 of valve 16 is formed flat and perpendicular to the valve axis. The spring seat 38 for spring 26 is provided with a flat mating surface 40 for engaging the flat end 39 of the valve to minimize the transfer of lateral thrust therebetween. An upward projection 42 on the spring seat 38 is closely received within the end of the spring 26 and the spring seat 38 is dimensioned to space its periphery from the wall of the spring chamber 28 by an annular clearance 41 to prevent contact between the spring seat 38 and the wall of the spring chamber. As a result, the spring seat 38 is laterally positioned solely by the spring 26 and is not susceptible to any seizure or binding due to cocking of the spring seat 38 or its engagement with the wall.

The stem 35 of the liftstop adjusting screw 34 is ground to provide a smooth surface to minimize the friction therebetween and is dimensioned to be received within the coils of the biasing spring 26 with a close sliding fit. By this construction, the lift stop serves as a pilot to control the lateral position of the spring which in turn serves to mount the spring seat 38 so that the spring seat is self-centering and imposes its biasing force along the axis of reciprocation of the valve 16 without imposing lateral forces thereon. Moreover, by guiding the spring 26 by the stem 35 of lift stop 34, lateral stability is imparted to the spring to avoid longitudinal bowing or buckling and to maintain its axis coincident with the axis of stem 35 and assure uniform operational characteristics of the spring 26 under all vibrational conditions.

By spacing the spring seat 38 from the bore of the walls, it is readily apparent that any cocking thereof, or any lateral movement thereof, will not cause its engagement with the walls of the spring chamber 28 and any resultant binding which will adversely affect the operation of the injector is avoided.

As shown in the drawing, the end of the sem 35 has a converging taper 44 at its end of, say, about 23 to accommodate a gradually increasing lateral movement of the surrounding coils of the spring 26 with respect to a stem 35 to provide a limited lateral resiliency to bias the spring seat 38 to a coaxial position, while at the same time making the spring seat free floating to enable it to align itself with the end of the valve without imparting lateral forces thereto. Preferably, and as shown, a convex radius 46 is formed at the upper edge of the projection 42 of the spring seat 38 to accommodate lateral shifting of the spring seat 38 without imposing a sharp termination of the portion of spring coils subject to lateral flexure.

From the foregoing, it is apparent that the present invention provides a new and improved inwardly opening pressure actuated injector in which a novel spring construction substantially aids in the promoting of the uniformity of the discharge of fuel from the nozzle by reducing the possibility of seizure or variations in mechanical friction between the valve and its guide or in the operational characteristics of the biasing spring.

As will be apparent to persons skilled in the art, various modifications, adaptations and variations of the foregoing specific disclosure can be made without departing from the teachings of the present invention.

1 claim:

1. A liquid fuel injector for delivering to the combustion chamber of an associated engine measured charges of liquid fuel comprising a tubular body having a bore provided with a valve seat and a discharge tip at one end thereof, a pressure operated inwardly opening valve disposed in said bore, an apertured valve guide mounting said valve for reciprocating movement toward and away from the valve seat, a spring chamber, a coil spring disposed in said spring chamber for biasing said valve toward said valve seat, a lift stop fixed to the injector body and having a stem extending into said coil spring to limit the axial movement of said valve from said valve seat, a spring seat engageable with the valve at the end remote from the valve seat and spaced from the wall of said spring chamber by an annular clearance, said spring seat being secured to the end of said spring for lateral movement in unison therewith and having a surface engageable with said valve for free lateral movement relative thereto, said stem having a cylindrical portion terminating in a free end portion provided with a converging taper, said coil spring engaging the cylindrical portion of said stem with a close sliding fit to fix the spring coaxial with the stem, said coil spring further being slightly spaced from said tapered end portion to bias the spring seat toward a coaxial po sition with the stem and maintain the spring seat out of contact with the wall of said spring chamber whereby the spring serves as the sole lateral support for the spring seat. I

2. The injector of claim 1 wherein said spring seat has a projection extending into the end of said spring and said projection terminates in a convex radius.

3. The injector of claim 1 wherein the mating surface of said valve and said spring seat are formed perpendicular to the longitudinal axis of said injector. 

1. A liquid fuel injector for delivering to the combustion chamber of an associated engine measured charges of liquid fuel comprising a tubular body having a bore provided with a valve seat and a discharge tip at one end thereof, a pressure operated inwardly opening valve disposed in said bore, an apertured valve guide mounting said valve for reciprocating movement toward and away from the valve seat, a spring chamber, a coil spring disposed in said spring chamber for biasing said valve toward said valve seat, a lift stop fixed to the injector body and having a stem extending into said coil spring to limit the axial movement of said valve from said valve seat, a spring seat engageable with the valve at the end remote from the valve seat and spaced from the wall of said spring chamber by an annular clearance, said spring seat being secured to the end of said spring for lateral movement in unison therewith and having a surface engageable with said valve for free lateral movement relative thereto, said stem having a cylindrical portion terminating in a free end portion provided with a converging taper, said coil spring engaging the cylindrical portion of said stem with a close sliding fit to fix the spring coaxial with the stem, said coil spring further being slightly spaced from said tapered end portion to bias the spring seat toward a coaxial position with the stem and maintain the spring seat out of contact with the wall of said spring chamber whereby the spring serves as the sole lateral support for the spring seat.
 2. The injector of claim 1 wherein said spring seat has a projection extending into the end of said spring and said projection terminates in a convex radius.
 3. The injector of claim 1 wherein the mating surface of said valve and said spring seat are formed perpendicular to the longitudinal axis of said injector. 